1. Technical Field
This invention relates generally to electronic components, and more particularly to a surface-mount light-emitting diode (LED) device.
2. Background Information
Recall that a surface-mount component usually mounts entirely on one side of a printed circuitboard. It does not rely on wire leads that extend through holes to solder pads on the reverse side. Instead, it relies on small terminals that lie directly on circuitboard traces. A thin film of solder holds them in place. That arrangement promotes miniaturization and facilitates fabrication.
But certain problems arise with existing surface-mount LED components. Consider, for example, the task of designing a front panel for a radio-controlled (R/C) speed controller. The speed controller mounts onboard an R/C model racing car where it controls motor operation according to commands received via an onboard receiver. Its front panel enables an operator to specify various operating parameters. The front panel may include a miniature keypad for that purpose as well as an indicator in the form of an LED. In the interest of small size, a surface-mount LED component may be selected. But mounting problems accompany that selection.
A typical existing surface-mount LED component is tiny. It may include a 0.4 mm or so square LED chip mounted on the upperside of a 0.6 mm thick base that measures about 1.3 mm wide and 3.0 mm long. A 9.0 mm high lens covers the LED chip so that a viewer can discern emitted light when facing the upperside of the base. Electrically conductive traces on the base form two terminal pads on the underside for connection to traces on a circuitboard.
To mount the surface-mount LED on a circuitboard, one positions the base so that the underside faces the circuitboard. In that position, the two terminal pads on the underside sit atop two traces on the circuitboard. The upperside of the base faces away from the circuitboard toward the direction of a viewer. However, that position can be a problem when the circuitboard serves as the front panel of an R/C speed controller because the surface-mount LED component projects outwardly from the front panel toward the viewer. It occupies a vulnerable position. It also frustrates efforts to maintain a flat front panel appearance.
Surface-mounting the LED component on the reverse side of the circuitboard so that it spans a hole through the circuitboard does not work because the LED component emits light away from the surface on which it is mounted. So, it emits light rearwardly when back-mounted--away from the circuitboard and viewer instead of through the hole toward the viewer. Thus, existing surface-mount LEDs do not adapt well to the application described.